add missed file

src/_pytest/paths.py

@@ -0,0 +1,13 @@
+from .compat import Path
+from os.path import expanduser, expandvars, isabs
+
+
+def resolve_from_str(input, root):
+    assert not isinstance(input, Path), "would break on py2"
+    root = Path(root)
+    input = expanduser(input)
+    input = expandvars(input)
+    if isabs(input):
+        return Path(input)
+    else:
+        return root.joinpath(input)